Pressure transducer and switch combination

ABSTRACT

A device for providing a plurality of indications of a select pressure, said device including: an electronic interface having an input and an output; a resistive structure adapted to measure the select pressure and being electrically coupled to the input of the electronic interface; a first output for providing a signal indicative of the select pressure, the first output being electrically coupled to the output of the electronic interface; and, a comparator coupled to the output of the electronic interface and being adapted to provide a signal indicative of whether the select pressure is greater than a predetermined threshold.

FIELD OF INVENTION

[0001] The present invention relates to pressure transducers andswitches, and more particularly a combination assembly thereof.

BACKGROUND OF INVENTION

[0002] In many applications, for example aircraft and helicopterinstallations, the measurement of pressure is of vital importance. Insuch examplematic installations, examples of specific cases are theengine oil pressure and hydraulics. Typically this information isconveyed to a pilot in two redundant ways. One by means of a transducerand a cockpit indicator, the second by a pressure switch and a warninglamp. In this way, even if one system fails, the pilot will have enoughinformation to correctly ascertain the present situation.

[0003] This arrangement proved necessary due to the low reliability ofthe older components used in the system: namely mechanical transducers,mechanical switches, indicators, lamps, wiring, etc. Modern systemsimproved the reliability in a significant way. One such example is thesolid state piezorezistive pressure transducer, which has a significantbetter reliability and accuracy than the older mechanical Bourdon typepotentiometer based transducers.

[0004] However, a weak link in this chain is the mechanical pressureswitch. Although possible to be replaced by a solid state piezorezistivedevice and suitable electronics, most installations still use mechanicaldevices. One major reason for this is the fact that existing wiringprovides only two conductors, while a solid state pressure switchrequires at least an additional one for a constant supply voltage forthe electronics.

[0005] The mechanical switches have another major disadvantage in thatthey are costly in the long run. Although individual mechanical switchesare less expensive than a solid state piezorezistive transducer, due toa high failure rate, they must be replaced significantly more often thana transducer, resulting in significant costs in materials and labor.

[0006] Accordingly it is an object of the present invention, which isdescribed below, to provide a convenient, reliable and cost effectivenew solution which does not require significant changes in the wiring ofthe plane, eliminates the unreliable mechanical switches and theassociated high cost.

SUMMARY OF THE INVENTION

[0007] A device for providing a plurality of indications of a selectpressure, said device including: an electronic interface having an inputand an output; a resistive structure adapted to measure the selectpressure and being electrically coupled to the input of the electronicinterface; a first output for providing a signal indicative of theselect pressure, the first output being electrically coupled to theoutput of the electronic interface; and, a comparator coupled to theoutput of the electronic interface and being adapted to provide a signalindicative of whether the select pressure is greater than apredetermined threshold.

BRIEF DESCRIPTION OF THE FIGURES

[0008]FIG. 1 illustrates a simplified diagram of a voltage outputtransducer presently utilized.

[0009]FIG. 2 illustrates a simplified diagram of a current outputtransducer presently utilized.

[0010]FIG. 3 illustrates a more complete illustration of the system ofFIG. 1.

[0011]FIG. 4 illustrates a transducer/switch voltage-transducercombination according to the present invention.

[0012]FIG. 5 illustrates a transducer/switch current-transducercombination according to the present invention.

DESCRIPTION OF THE INVENTION

[0013] A simplified diagram of a voltage output transducer presently inuse is illustrated in FIG. 1. Therein a pressure transducer 10 providesa 0-5 V signal which is displayed to a pilot using a pressure indicator20. Further a pressure switch 30 (which is preferably normally-closed)provides a signal source to a warning lamp 40. A simplified diagram of acurrent output transducer presently in use is illustrated in FIG. 2.Therein a pressure transducer 50 provides a 4-20 mA signal which isdisplayed to a pilot using the pressure indicator 20. Further thepressure switch 30 (again, which is preferably normally-closed) providesa signal source to the warning lamp 40. In these ways the systems asillustrated in FIGS. 1 and 2 can be seen to provide redundantinformation to a pilot.

[0014]FIG. 3 illustrates a more complete schematic of the system of FIG.1, wherein like references refer to like elements, and which includes aLamp Test Switch 60, associated diodes 70, and an adjustable supplyvoltage 80 for the lamp(s) for dimming purposes. As is understood bythose possessing ordinary skill in the art, a more detailed diagram fora current output transducer is similar.

[0015] The proposed invention of a transducer-switch combination isshown in FIG. 4 (voltage output transducer system 100) and FIG. 5(current output transducer system 200). It combines the transducer andswitch functions and electronics in one reliable unit. It makes use ofthe existing supply voltage present in the transducer to supply voltageto the switch circuitry. In the case of current output transducers, italso makes use of the high impedance piezorezistive bridge inherentlyneeded for such design and low power associated electronics for theswitch function.

[0016] The transducer interface 110 is any of the configurationsdescribed in numerous previous patents, ______, which are well known inthe art. All have an inherent high level voltage which is used as aninput 140 to a comparator 130. The other input 150 to the comparator 130is an adjustable voltage which sets the switch trip point. An additionalbuffer op-amp 160 is provided in case of malfunction of the indicator(i.e. short circuit). Even in such instance the operation of the switchand lamp is not affected. Not shown in the drawings, but described inprevious patents, are means of adjustment of the hysteresis. Suchadjustment is particularly difficult or impossible for mechanicalswitches.

[0017] The current output devices, i.e. 4 to 20 mA sources, areextremely advantageous. This combination uses only three wires toimplement both functions: transducer and switch.

[0018] The comparator 130 is preferably a very low power operationalamplifier, e.g. a CMOS device. It is also possible to use a truecomparator which already incorporates an open collector output. Using anoperational amplifier makes the setting and/or adjustment of thehysteresis much easier.

[0019] The circuit described herein can be seen to provide significantadvantages. For example, it adds very few components to existingtransducer electronics, and all the added components have an extremelygood reliability and relatively low cost. The overall reliability istherefore not less than the excellent reliability of the solid statepiezorezistive transducer. Further, the cost of the new combination isalmost the same as the cost of the transducer alone, while the switchand its associated high cost are eliminated. Further yet, the new systemis fully compatible with existing aircraft wiring and associatedfunctions (i.e. Lamp Test, dimming, etc.).

[0020] The proposed Pressure Transducer and Switch Combination may havedifferent output configurations than those shown. FIG. 4 illustrates abipolar NPN transistor open collector configuration 170, while FIG. 5illustrates a N-channel MOSFET open drain output configuration 180. Alsopossible are high side switches (the FIGS. 4 and 5 show low sideswitches), normally-open switches, multiple trip point switches, etc.

[0021] Although the invention has been described in a preferred formwith a certain degree of particularity, it is understood that thepresent disclosure of the preferred form has been made only by way ofexample, and that numerous changes in the details of construction andcombination and arrangement of parts may be made without departing fromthe spirit and scope of the invention as hereinafter claimed. It isintended that the patent shall cover by suitable expression in theappended claims, whatever features of patentable novelty exist in theinvention disclosed.

We claim:
 1. A device for providing a plurality of indications beingreflective of a select pressure, said device comprising: an electronicinterface having an input and an output; a resistive structure adaptedto measure said select pressure and being electrically coupled to saidinput of said electronic interface; a first output for providing asignal indicative of said select pressure, said first output beingelectrically coupled to said output of said electronic interface; and, acomparator coupled to said output of said electronic interface and beingadapted to provide a signal indicative of whether said select pressureis greater than a predetermined threshold.
 2. The device of claim 1,wherein said electronic interface further includes a second outputcoupled to said resistive structure, said second output being adapted toprovide a supply voltage to said resistive structure.
 3. The device ofclaim 2, wherein said resistive structure comprises a plurality ofpiezoresistive devices coupled in a wheatstone bridge configuration. 4.The device of claim 1, further comprising an amplifier including firstand second inputs, wherein said first input of said amplifier is coupledto said output of said electronic interface and said second input ofsaid amplifier is coupled to said output of said amplifier.
 5. Thedevice of claim 1, further comprising a transistor coupled to saidcomparator.
 6. The device of claim 5, wherein said comparator includesfirst and second inputs and an output, wherein said first input of saidcomparator is coupled to said output of said electronic interface andsaid output of said comparator is coupled to said transistor.
 7. Thedevice of claim 6, wherein said transistor is coupled to a means forindicating when said signal indicative of whether said select pressuredrops below said predetermined threshold.
 8. The device of claim 7,wherein said second input of said comparator is coupled to an adjustablevoltage being associated with said predetermined threshold.
 9. A devicefor indicating a pressure to a pilot of an aircraft, said devicecomprising: a sensor structure adapted to measure said pressure; meansfor interfacing with said sensor structure, said means being coupled tosaid sensor structure; and, a comparator coupled to said means; whereinsaid means is adapted to provide a first signal indicative of a value ofsaid pressure to said pilot, and said comparator is adapted to provide asecond signal indicative of whether said value of said pressure dropsbelow a predetermined threshold.
 10. The device of claim 9, wherein saidelectronic interface is further adapted to provide a supply voltage tosaid sensor structure.
 11. The device of claim 10, wherein said sensorstructure comprises a plurality of piezoresistive devices coupled in awheatstone bridge configuration.
 12. The device of claim 9, furthercomprising an amplifier including first and second inputs and an output,wherein said first input of said amplifier is coupled to said means andsaid second input of said amplifier is coupled to said output of saidamplifier.
 13. The device of claim 9, further comprising a transistorcoupled to said comparator.
 14. The device of claim 13, wherein saidcomparator includes first and second inputs and an output, wherein saidfirst input of said comparator is coupled to said means and said outputof said comparator is coupled to said transistor.
 15. The device ofclaim 14, wherein said transistor is coupled to a means for indicatingwhether said select pressure drops below said predetermined threshold.16. The device of claim 14, wherein said second input of said comparatoris coupled to an adjustable voltage being associated with saidpredetermined threshold.
 17. A method for upgrading a pressureindicating system for an aircraft comprising the steps of: providing asensor structure adapted to measure a select pressure in a suitableposition; coupling an input of an electronic interface to said sensorstructure; providing a first output for producing a signal indicative ofsaid select pressure, said first output being electrically coupled tosaid output of said electronic interface; and, coupling a comparator tosaid output of said electronic interface, said comparator being adaptedto provide a signal indicative of whether said select pressure dropsbelow a predetermined threshold.
 18. The method of claim 17, whereinsaid sensor structure comprises a plurality of piezoresistive devicescoupled in a wheatstone bridge configuration.
 19. The method of claim17, further comprising an amplifier including first and second inputs,wherein said first input of said amplifier is coupled to said output ofsaid electronic interface and said second input of said amplifier iscoupled to said output of said amplifier.
 20. The method of claim 17,wherein said comparator includes first and second inputs and an output,and said method further comprises the steps of: coupling said firstinput of said comparator to said output of said electronic interface;coupling said output of said comparator to a transistor; and, supplyingan adjustable voltage being associated with said predetermined thresholdto said second input of said comparator.